Generally, the output torque of a rotary machine, such as a motor, is transformed into driving force acting in a driving direction by combining a linkage, and belts or ropes with rotating members to drive a driven object for linear motions by the rotary machine. In such a system, if the rotating member is eccentric relative to a support mechanism with its axis of rotation not aligned with the axis of the support mechanism or if the center of gravity of the rotating member is not on the axis of rotation of the rotating member and the rotating member is dynamically unbalanced, the system vibrates and it is difficult to drive the driven object for desired movement. For example, in an elevator system, all the components of the elevator system driven by a motor are caused to move vertically in phase, and an elevator car included in the elevator system is vibrated vertically in synchronism with the rotation of the dynamically unbalanced rotating member to spoil ride quality.
Since the vibration mode of such in-phase vibrations of the components of the system is different from that of a rotating motion, the in-phase vibrations cannot be suppressed through the control of the torque of the motor. Therefore, a generally known in-phase vibration suppressing method improves the mechanical accuracy of the rotating member so that the eccentricity and dynamic unbalance of the rotating member may not be sources of vibrations. However, the method of improving the mechanical accuracy needs time for processing the rotating member and incorporating the rotating member into the system and hence increases the cost of the system.
The conventional in-phase vibration suppressing method needs to process rotating members included in a system highly accurately and to install the same highly accurately, needs to use material resistant to aging and fatigue due to vibrations, and needs to process the rotating members by advanced techniques. Consequently, the cost of the system increases inevitably to satisfy the desired ability and reliability of the system.